Watch the night sky long enough and you'll notice the stars slowly drifting. They rise in the east, arc across the sky, and set in the west, just like the Sun. Time-lapse photos turn them into glowing circles. But one star near the center of those circles hardly seems to move at all.
That's Polaris, the North Star. It lies almost directly in line with Earth's axis, the imaginary rod our planet spins around, above the North Pole. As Earth turns, the other northern stars appear to wheel around that point, while Polaris stays nearly fixed. It does move a tiny bit, though, as you'll see.
It's Earth That's Doing the Moving
The stars aren't really circling us. Earth is spinning, and that makes the whole sky appear to rotate. Picture sitting on a merry-go-round and looking straight up at the center of the ceiling. Everything around the edge seems to swing past, but the spot right above the pole barely shifts.
Polaris sits less than one degree from that spot, called the north celestial pole. Because of that, it makes only a tiny circle each night, about 1.3 degrees across. To the naked eye, it looks as if it's standing still.
A Sailor's Best Friend
A star that stays put is a gift for navigation. If you can find Polaris, you can find north. Even better, its height above the horizon gives you your approximate latitude. In Old English it was even called "scip-steorra," or ship-star.
Navigators still had to be careful. On his first voyage across the Atlantic in 1492, Christopher Columbus had to correct for the small circle the pole star makes around the pole.
And here's a surprise: Polaris is not the brightest star in the night sky, as many people believe. It ranks only around 47th among the brightest stars we can see. It's famous for where it is, not how bright it is.
The North Star Changes Over Time
Earth's axis wobbles very slowly, like a spinning top, in a motion called precession. One full wobble takes about 26,000 years. As it happens, the point in the sky that the axis points to slowly drifts from star to star.
Around 3000 BC, the North Star was a faint star called Thuban, in the constellation Draco. It sat even closer to the pole than Polaris does today, but it's only about one-fifth as bright and is hard to see in city skies. In the time of ancient Greece and Rome, there was no bright star right at the pole at all.
That makes a famous line from Shakespeare a little funny. In his play Julius Caesar, written around 1599, Caesar calls himself "as constant as the northern star." In Caesar's actual lifetime, there was no constant northern star.
Polaris's Best Years Are Coming
Right now, Polaris is getting even closer to the pole. It will be at its closest soon after the year 2100. After that, the pole will slowly move away, passing near the stars Errai, Deneb, and eventually Vega in about 14,500 AD.
So on your next clear night, look north and find that steady little light. It has guided travelers for centuries, and it will keep doing the job long after all of us. Just don't expect it to keep the title forever.
